This invention relates to radio frequency communication systems for communication of signals into a media. More specifically, the present invention relates to a synchronized communication system for communication of radio signals into an underground environment.
Electromagnetic waves with a radio frequency have been used in the past to transmit information between remote locations. Such electromagnetic waves, often referred to as radio waves or radio signals, propagate well through the air, but in general do not propagate well through man-made structures, such as large buildings, or into the body of the earth.
However, it has been known in the past that radio signals having a lower frequency, generally below 300 KHz, propagate better through a medium such as the body of the earth or large man-made structures, than radio signals having higher frequencies. In fact, low frequency radio signals have been known to propagate several thousand feet, or two to three kilometers, into the earth. In addition, low frequency radio signals have been used to carry information to remote locations either under the ground or in large man-made structures. However, in order to generate low frequency radio signals that can propagate through the earth, it is generally necessary to have a fairly large antenna, such as an antenna approximately 10 meters to 150 meters in diameter, as well as a signal generator that can generate a signal at a sufficient power output to reach the surface. While it is possible to have an antenna of this size located on the surface of the earth, it is generally difficult to have antennas of this size and power output located underneath the earth or within man-made structures. Also, it would not be possible for such an antenna to be made portable so that it can be carried by an individual. This results in it being possible to transmit low frequency radio signals into underground environments or into large man-made structures, but it is difficult to then transmit low frequency radio signals out of underground environments or man-made structures simply because it is not practical to have antennas and signal generators with such large diameters and power outputs in these environments, or, to have them mobile.
Accordingly, in the past, several types of communication systems utilizing low frequency radio signals have been proposed. However, all of these prior art systems provide for communication into the medium, but do not provide for easy communication of radio signals out of the medium. In particular, low frequency communication signals for communication to underground environments, such as in mines, have been proposed in the past. However, these low frequency communication systems generally are used to propagate alert signals or warnings into the underground environment, but do not provide easy transmission of information out of the underground environment.
Accordingly, there is a need in the art for a communication system for communicating radio signals to, as well as from, remote transceivers located within a medium through which radio signals generally do not propagate well. In particular, there is a need in the art for a radio frequency communication system for communicating radio signals to and from remotely located transceivers utilizing a low frequency radio signal, but not requiring large antennas or powerful signal generators located within the medium.
Accordingly, it is an object of this invention to at least partially overcome the disadvantages of the prior art. Also, it is an object of this invention to provide an improved type of communication system which can use low frequency radio signals to transmit information to and from remote transceivers located within the medium.
Accordingly, in one of its objects, this invention resides in a radio frequency communication system for communicating radio signals, said communication system comprising:
a central station comprising a transmitter for transmitting a synchronization signal at a low radio frequency into a medium, and, a receiver for receiving radio signals from the medium;
a remote transceiver located within the medium for receiving the low frequency synchronization signal and transmitting an information radio signal to be received by the central station; and
wherein the information radio signal is synchronized in time with the low frequency synchronization signal.
In a further aspect, the present invention resides in a radio frequency communication system for communicating information from and to remote transceivers located within a medium by way of radio signals, said communication system comprising:
a central station comprising a transmitter for transmitting a low frequency radio signal into the medium, and, a receiver for receiving information signals from the medium;
a zone transceiver located within a zone of the medium for receiving the low frequency radio signal and transmitting a zone information radio signal in response to and synchronized in time with the low frequency radio signal; and
wherein the zone information radio signal is indicative of information received by the zone transceiver from remote transceivers located within the zone.
In a still further aspect, the present invention resides in a method of communicating information to and from remote transceivers located within a medium by way of radio signals, said method comprising the steps of:
transmitting a low frequency radio signal into the medium from a central station;
receiving the low frequency radio signal at a zone transceiver located within a zone of the medium;
transmitting a zone information radio signal from the zone transceiver to the central station in response to, and synchronized in time with, the low frequency radio signal; and
wherein the zone information signal is indicative of information received by the zone transceiver from transceivers located within the zone.
One advantage of the present invention is that by having the signals emanating from transceivers within the medium synchronized with the low frequency radio signal being transmitted into the medium, the specific time at which the information signals from within the medium should be received by the central station can be determined. In other words, the receiver at the central station can be designed to receive the signal at specific time periods, thereby improving the reception of the information radio signals emanating from transceivers within the medium. This permits the central station to receive radio signals having a much lower power output and also at a higher frequency. Radio signals of this type can be easily generated by mobile transceivers having relatively small antennas.
A further advantage of the present invention is that the synchronization of the information radio signals emanating from transceivers within the medium can be used to assist in filtering noise from the information radio signals. In other words, because it is known that the information signals from transceivers in the medium should be received at precise time periods, more advanced filters, such as filters which perform Laplace transformations, Fourier transformations, or a combination of both, can be utilized to minimize the noise to signal ratio of the information signals being transmitted from transceivers within the medium.
A further advantage of the present invention is that, because the system improves the reception of signals being transmitted from transceivers within the medium, the transceivers can be used to transmit information of a more sensitive nature, such as information regarding the control and monitoring of equipment within the medium.
A further advantage of the present invention is that zone transceivers can be used within the medium to amplify and retransmit signals received from transceivers within the zone of the zone transceivers. In this way, zone transceivers can extend the electromagnetic signal coverage of the low frequency transmitter and receiver located outside of the medium. The zone information signals transmitted by the zone transceivers will be synchronized in time with the low frequency radio signal, and therefore will also be received more easily by the receiver at the central station. In addition, where more than one zone transceiver is used, each zone transceiver can be synchronized with the low frequency radio signal.
A still further advantage of the present invention is that the low frequency synchronization radio signal can be modulated. In this way, information can be transmitted from the central station to the transceivers. Also, the central station can modulate the synchronization signal to poll or address a specific transceiver or send information, such as instructions, to a specific transceiver. In one embodiment, a part of the modulated synchronization signal can be reserved for receiving information radio signals from any one of the transceivers indicating an emergency or alert within the mine.
A further advantage of the present invention is that all radio signal communication within the medium can be synchronized by the low frequency radio signal. In this way, communication between transceivers within the medium can be improved, even though the communication signals are not transmitted outside of the medium, simply because the information signals being transmitted between the various transceivers within the medium is synchronized, and therefore improved filtering and reception are possible.
Further aspects of the invention will become apparent upon reading the following detailed description and drawings which illustrate the invention and preferred embodiments of the invention.